1. Field of the Invention
The present invention relates to a light source apparatus and a projector.
Priority is claimed on Japanese Patent Application Nos. 2003-365008 and 2003-365009, filed Oct. 24, 2003, No. 2004-15702, filed Jan. 23, 2004, and on No. 2004-196558 filed Jul. 2, 2004 the contents of which are incorporated herein by reference.
2. Description of Related Art
In recent years, projectors have achieved advances in miniaturization, higher levels of brightness, length of lifespan, cost reduction, and the like. For example, as regards miniaturization, the size of a liquid crystal panel (i.e., an optical modulator) has dropped from 1.3 inches diagonally to 0.5 inches diagonally, with a size reduction of slightly more than ⅙ being achieved in the surface ratio.
A reduction in the size of a projector obtained by using a light emitting diode (LED) light source, which is a solid state light source, as the light source of the projector has been proposed. LED light sources are small in size and include a power source, and have merits as light sources for projectors such as their ability to be turned on and off instantaneously, their broad color reproducibility, and their long life span. In addition, because they contain no harmful substances such as mercury, they are preferable from the standpoint of environmental protection.
However, because the brightness thereof is insufficient as a light source, in order to use an LED light source as the light source of a projector, it is necessary to secure (i.e., to increase the intensity and to reduce the etendue) a brightness of at least the level of a discharge type of light source lamp. Here, the term “etendue” refers to a numerical value that shows a spatial expanse in which luminous flux that can be effectively used is present expressed as the product of a surface area and a solid angle. Moreover, the etendue is optically preserved. As is described above, because a reduction in the size of liquid crystal panels has been achieved and the etendue of liquid crystal panels has been reduced, it is also necessary to make the etendue of the light source either equivalent or smaller.
However, as the level of brightness of LED light sources has increased, the heat output from LED light sources has also further increased. However, if the temperature of an LED light source rises, the light emission efficiency thereof deteriorates so that some type of heat output countermeasure has been required. In the forced air-cooling system using a fan that is generally employed, the cooling effect is insufficient and the noise from the fan has created problems. For this reason, methods of forcibly cooling an LED light source using a liquid have been proposed, for example, in Japanese Unexamined Patent Application, First Publication (JP-A) Nos. H06-5923 and H07-99372. From a liquid cooling method, an effect of nullifying the noise generated in the forced air-cooling system is also anticipated.
In the LED light source disclosed in JP-A No. H06-5923, by circulating a cooling material such as liquid nitrogen or the like around the LED, the LED and the cooling material are placed in direct contact with each other so as to achieve forced cooling. However, because the structure of the LED light source is complex due to an insulating case being necessary and the like, the manufacture thereof is not practical. Therefore, the problem arises that it is difficult to secure at the least the brightness level of a discharge type light source lamp.
In the LED light source disclosed in JP-A No. H07-99372, the periphery of an LED chip (i.e., the light emitting chip) is filled with an insulating inert liquid so as to cool the LED chip. However, a device for positively cooling the insulating inert liquid is not provided so that the cooling effect is low and it is difficult to cool an LED chip for an extended period of time. Consequently, the problem arises that it is difficult to secure at the least the brightness level of a discharge type light source lamp.
Moreover, when an LED light source is being driven by a large current, it is necessary to consider the electrical resistant of wiring and the like, which in a conventional LED light source has not been a problem. Specifically, in the LED light source disclosed in Japanese Unexamined Utility Model Application, First publication (JP-U) No. H06-9158, current is inject via bonding wire made of gold or the like into a light emitting chip that generates light and heat when energized. When the LED light source is driven by a large current, because of the electrical resistance of the bonding wire there is a concern that the bonding wire will generate heat and melt, resulting in a broken wire. Furthermore, small diameter wiring heats up and generates an extra load on the cooling system so that, as a result, there is a concern that the heat discharge effect for the LED light source will be worsened.
In a light source apparatus that is provided with an LED light source such as those described above, generally, in order to improve the extraction efficiency of generated light, as is shown, for example, in JP-A Nos. H07-7185 and H11-65477, generated light that is emitted in an oblique direction relative to the direction of emission from the light emitting chip is reflected in the direction of emission of the light source apparatus using reflectors that are placed around the light emitting chip. As a result of providing reflects such as these, generated light that is emitted from the light source apparatus is changed into parallel light, and it is possible to further increase the utilization efficiency of the light.
If a light source apparatus is used as the light source for a projector, it is necessary to change the generated light into parallel light and then irradiate it onto an optical modulator of the projector. However, as is described above, because the miniaturization of liquid crystal panels (i.e., of optical modulators) has advanced and the etendue of liquid crystal panels has become smaller, it has also become necessary to lower the etendue of light source apparatuses for projectors as well. Note that here the term “etendue” is a parameter given by the product of the light emitting surface area of a light source and the solid angle that can be condensed, and shows a spatial expanse in which luminous flux that can be effectively used is present. The etendue is optically preserved.
Because a conventional light source apparatus reflects generated light that is emitted in an oblique direction from the front surface of a light emitting chip is reflected by a reflector in the emission direction of the light source apparatus, it is possible to change the generated light that is emitted from the front surface of the light emitting chip into parallel light. However, generated light is also emitted from surfaces other than the front surface of a light emitting chip, and in a conventional light source apparatus, this generated light is also reflected by the reflector. Accordingly, in a conventional light source apparatus, there is a large amount of etendue, and it is difficult to change all of the generated light that is emitted from side surfaces of a light emitting chip into parallel light and this light into a miniaturized liquid crystal panel (i.e., optical modulator). As a result, a large amount of generated light that is emitted from side surfaces of a light emitting chip becomes stray light inside a projector after it has been emitted from the light source apparatus.
Moreover, in a projector, in order to improve display characteristics, it is preferable that the illumination intensity of the generated light that is irradiated onto the optical modulator is uniformly distributed. However, because it is difficult to match generated light that is emitted from side surfaces of a light emitting chip such as that described above with generated light that is emitted from the front surface of the light emitting chip, and then make this light uniform and emit it, the illumination intensity of generated light that is emitted from a light source apparatus is not uniformly distributed.
The present invention was conceived in view of the above described problems and a first object thereof is to provide a light source apparatus whose structure can be simplified and in which it is possible to efficiently cool a light emitting chip, and to further provide a projector that is bright and has an excellent display quality.
A second object of the present invention is to prevent breakages in electrode wires.
A third object of the present invention is to reduce excess load on a cooling system and to improve a heat discharge effect of an LED light source by preventing unnecessary heat output that is caused by electrical resistance of the electrode wires.
A fourth object of the present invention is to lower the etendue of a light source and to uniformly distribute the illumination intensity of generated light that is output from a light source apparatus by eliminating the generated light component that is emitted from side surfaces of a light emitting chip.